Method for lightening residual oil

The invention discloses a method for lightening residual oil. According to the method, residual oil raw materials goes through a hydrotreatment device, and the obtained hydrogenated oil undergoes flash evaporation to obtain light components and heavy components; the heavy components enters a reduced pressure distillation device to separate out reduced pressure wax oil, and the reduced pressure wax oil which is mixed with the hydrogenated light components enters a catalytic cracking device and undergoes fractionation to obtain a gas, gasoline and diesel oil which are discharged form the catalytic cracking device and recycle oil and oil slurry which are returned to the hydrotreatment device; and reduced pressure residual oil obtained by the reduced pressure distillation device enters a delayed coking device and undergoes the fractionation to obtain a gas, gasoline and a diesel oil fraction which are discharged from the delayed coking device and coked wax oil and tail oil which are returned to the hydrotreatment device. The method which combines the residual oil hydrotreatment, the catalytic cracking, the reduced pressure distillation and above delayed coking technology allows charged material compositions of the residual hydrogenation, the catalytic cracking and the delayed coking to be optimized, and target product yields of the catalytic cracking and the delayed coking to be improved.